British Pat. No. 436,774 (Greenside and Irwell Rubber Co., Ltd., 1935) describes and claims a process for tightly sewing together fabric webs. The webs are bonded together at the edges externally and at the same side, spread apart, externally sewn at the edge in the adhesive layer, the edge with the layer then being wrapped around and bonded to an outer face of the web. Thus, on one side of the seam, the stitches are located in the adhesive which should lead to a waterproof joint. Any tensile stress to which the joint is subjected is exclusively taken up by the bond and the sewn seam does not contribute in any way to the tensile strength of the joint. Pressure tightness is neither sought nor obtained in the process described in this British patent. Furthermore, one side of the seam always comes to rest at the top and must therefore be separately bonded over as, otherwise, there would be a risk of the threads ripping open.
British Pat. No. 977,367 (The Coventry Hood and Side Screen Co., Ltd., 1964) relates to a process for joining fabric webs which are coated on both sides in a waterproof manner.
As a result, it is possible to (a) arrange the webs in a flush manner one above the other, (b) sew them together at the edge, (c) fold the upper web over the seam, and (d) seal the plastic coating in the seam area.
With this process, the resulting seam exhibits considerable uneveness, both on the inside and the outside, which is particularly unacceptable if the joined fabrics are to be used in making shoes. Additionally, this process is based on the use of fabric which is coated on both sides, such fabric not being suitable for use in articles of clothing or shoes. Still further, the seam is unable to withstand tensile stresses.
The above described process using fabric which is coated on one side, according to FIGS. 1 and 2 of the first-mentioned British patent, leads to unsound and less strong joints. The description thereof makes no reference to the degree of pressure tightness of the joint.
It is possible to use a conventional method of joining polyurethane coated fabric materials by sewing and to them provide the seam with an adhesive strip. However, this type of joining such materials is never tight, not even against water acting with little or no pressure, e.g., rain or puddles. Without such adhesive tape, the water passes through the seam holes and with an adhesive tape the water which has entered through the seam holes diffuses relatively rapidly between the adhesive tape and the inside of the fabric material.